The objective of the invention is a method of straining a diaphragm and a device therefor.
Strained diaphragms are e.g. used in pressure sensor diaphragms, especially in diaphragms of a capacitive differential symmetric pressure sensor, and in microphone diaphragms. Microphones, that change the pressure variations of the acoustic waves into current amperage, have to be made very accurately, as even small pressure variations in the diaphragm have to be considered. In pressure sensors measuring extremely small pressure variations, e.g. 10 Pa, the diaphragm which moves with the pressure variations, has to be correctly strained. In these applications the even strain of the diaphragm throughout its whole surface is essential. Different methods are used to attach and strain such diaphragms. In one prior art solution, the diaphragm is attached between two rings placed within each other. The diaphragm is initially placed on top of e.g. one ring. Thereafter the rings are placed within each other. The internal diameter of the one ring is essentially the same as the exterior diameter of the other ring. The inner ring is provided with a female thread. The diaphragm is pressed between the external surface of the one ring and the internal surface of the other ring. The measurements of the rings must be accurate in order not to tear the thin diaphragm, and the mechanical manufacture of these parts requires accurate devices and adaptions.
In another method, as presented in FIG. 1, the diaphragm is placed on top of a ring provided with a female thread, and the diaphragm can be welded on top of the ring. The method requires special equipment for the welding of the thin diaphragm.
In the rings described above, the diaphragm 3 is attached to the ring 21 in the ways described above, and the ring 21 is provided with an interior female thread, by which it is further fastened to the male thread 27 of the frame 22, which can be a bush. When the ring 21, to which the diaphragm 3 is attached, is screwed into the bush 22, by its male threads 27, the diaphragm 3 touches the surface 26 of the bush 21 close to the closed-position, and by further screwing the bush, the diaphragm is strained to its desired tension. In these methods, really accurate measures are required for e.g. the dimensions of the rings or bushes, the threads, the shapes of the rings. etc., in order not to tear the diaphragm and to attach the ring and the frame within each other. Expensive devices are also required for the manufacture of the rings and the plate. The even straining of the diaphragm has especially created a problem. The diaphragm is strained by turning the bush 22 horizontally in relation to the ring 21, and the diaphragm is strained against the surface 26, by which the diaphragm of the present invention might move in the turning direction of the bush on the surface 26, which in turn might wrinkle the diaphragm.
The SE-patent 226781 presents a solution, in which a resilient body is placed between the diaphragm and the frame so that the diaphragm is not provided between the grooved member and the resilient body.